The present invention relates generally to compositions produced from .alpha.,.beta.-unsaturated dicarboxylic compounds and olefinically unsaturated compounds, which compositions possess properties making them particularly suitable for use as lubricants and lubricant additives.
Compositions comprising reaction products of .alpha.,.beta.-unsaturated dicarboxylic compounds and olefinically unsaturated compounds are generally known in the art. These reaction products have been described in the literature as having a large number of uses ranging from lubricants to emulsifiers, coating additives to cosmetics, protective colloids to dispersants, and detergents to plasticizers.
One particular type of such reaction products, i.e. intermediates in the production of polycondensation products, is known from GB 1 173 643. This reference discloses a specific, high pressure process which produces unsaturated tetracarboxylic acids by reacting an olefin with a 1,2-unsaturated 1,2-dicarboxylic acid or a functional derivative thereof. Suitable reactants to produce the tetracarboxylic acids are lower alkyl olefins. Preferred are branched olefins, with the olefin exemplified being isobutene.
The prior art further describes several schemes for reacting .alpha.,.beta.-unsaturated dicarboxylic and olefin compounds; however, the compositions produced by these known reaction schemes comprise essentially one or both of only two types of reaction products--lower molecular weight ene (alkenyl succinic) products and higher molecular weight polymerization products.
When reacting .alpha.,.beta.-unsaturated dicarboxylic compounds with olefins, the difference between producing the lower molecular weight alkenyl succinic product and the higher molecular weight polymerization products is normally due to the presence or absence of a polymerization initiator in the reaction mixture.
For example, U.S. Pat. No. 4,192,930, DE-A-3223694, EP-B-0075216 and JP Laid-Open 80/157687 (all of which are incorporated by reference herein for all purposes) teach the production of the higher molecular weight polymerization products by reacting .alpha.,.beta.-unsaturated dicarboxylic compounds and olefins in the presence of polymerization initiators such as peroxy compounds.
On the other hand, U.S. Pat. No. 3,381,022 (incorporated by reference herein for all purposes) teaches the production of alkenyl succinic compounds (and the hydrogenated alkyl succinic corresponding compounds) by reacting the above-mentioned components without the polymerization initiator.
To improve the efficiency of the ene reaction and increase selectivity toward the alkenyl succinic products, U.S. Pat. No. 3,819,660, U.S. Pat. No. 4,255,340, U.S. Pat. No. 4,396,774 and U.S. Pat. No. 4,761,488 (all of which are incorporated by reference herein for all purposes) teach the reaction of .alpha.,.beta.-unsaturated dicarboxylic acids and anhydrides with olefins in the presence of particular ene reaction catalysts (accelerators).
To achieve like results in increasing selectivity toward alkenyl succinic anhydrides, U.S. Pat. No. 3,412,111, U.S. Pat. No. 4,581,464 and JP Laid Open 82/32276 (all of which are also incorporated by reference herein for all purposes) teach the addition of a particular polymerization inhibitor to the reaction of .alpha.,.beta.-unsaturated dicarboxylic anhydrides and olefins. As indicated in the examples of U.S. Pat. No. 3,412,111, the use of the polymerization inhibitor does indeed appear to significantly improve selectivity toward the alkenyl succinic product.
Long chain hydrocarbyl polysuccinic anhydrides are known from U.S. Pat. No. 4,720,555, in which a method is disclosed which comprises the reaction of a long chain hydrocarbon with an excess of maleic anhydride in the absence of a solvent.
Further it is mentioned that a process for the preparation of substituted carboxylic acids wherein a mono olefin is reacted with an unsaturated, conjugated dicarboxyl compound is known from GB 954 901. The obtained products are useful as rust inhibitors in lubricating oils.
It should be noted that generally .alpha.,.beta.-unsaturated dicarboxylic acid esters are recognized to be less reactive with olefins than their acid and anhydride counterparts. This prejudice to the use of esters in an ene selective reaction scheme is also apparent from previously mentioned GB 1 173 643. The unsaturated carboxylic compounds exemplified therein, diethyl esters of maleate and fumarate, do react to form the specific tetracarboxylic acid, but the conversion is poor. Previously mentioned GB 954 901 makes a distinction between various carboxylic compounds and, in line with further prior art, does not actually make use of esters, teaching that carboxylic anhydrides are to be preferred. In view of their low reactivity, esters are further utilized only in the polymerization reactions as described, for example, in previously incorporated DE-A-3223694.
It has now surprisingly been discovered that, using the appropriate esters and olefins, compositions can be prepared as is further described below which comprise a substantial amount of an intermediate molecular weight reaction product which is neither the known lower molecular weight alkenyl succinic nor the known higher molecular weight polymeric reaction product.